import type { AsyncIndexedMapper, IndexedMapper } from '@naturalcycles/js-lib/types';
import type { TransformOptions, TransformTyped } from '../stream.model.js';
/**
 * Similar to RxJS `tap` - allows to run a function for each stream item, without affecting the result.
 * Item is passed through to the output.
 *
 * Can also act as a counter, since `index` is passed to `fn`
 */
export declare function transformTap<IN>(fn: AsyncIndexedMapper<IN, any>, opt?: TransformOptions): TransformTyped<IN, IN>;
/**
 * Sync version of transformTap
 */
export declare function transformTapSync<IN>(fn: IndexedMapper<IN, any>, opt?: TransformOptions): TransformTyped<IN, IN>;